Leon Lin was ecstatic when he found out he’d be leaving home in southern China to study at the University of Connecticut. As the Chinese agent whom his parents paid $5,000 to help him get into the school told him, the university’s flagship campus at Storrs was a highly ranked institution, with 25,000 students and ready access to Boston and New York City. And eventually Lin would return home with the status and career advantage of a U.S. degree.